UNUSUAL PHYSICAL-PROPERTIES OF KCU7-XS4 AT DIFFUSIVE ONE-DIMENSIONAL ORDERING TRANSITIONS

Single crystals of quasi-one-dimensional sulfides KCu7-xS4 with x = 0. 00, 0.12, and 0.34 were prepared by electrochemical methods. Temperatu re-dependent properties of resistance, thermal conductivity, thermoele ctric power, and heat capacity C-P Were Studied on single-crystal samp les. These measurements show several anomalies which we associate with phase transitions, with the transition temperatures and physical prop erties depending strongly on x. Most interestingly, measurements of C- P, with an ac technique show very unusual hysteresis and frequency dep endence. The present work indicates that these phase transitions are d ue to vacancy ordering involving Cu+-ion diffusion along the Cu(2)-Cu( 2) zigzag chains.